The objective of this research program is to obtain a clearer understanding on the interaction of leukemia virus and leukemia cells at the cellular level. Further properties on the Gross virus-induced murine leukemia cells cultured in vitro are proposed. The studies are aimed at understanding the phenomenon of repression and derepression of C-type viral replication in murine leukemia cells. Studies on the attempts to maintain aad propagate normal murine and human lymphoid cells are proposed. In the murine system, cultures will be exposed to the murine leukemia viruses on the attempt to induce morphological conversion.